1. Field of the Invention
This invention pertains to improvement in subterranean slurry mining and more particularly relates to a method for drilling and mining one or more layers of granular ore, such as phosphates, without withdrawing the mining apparatus from the hole between the drilling and mining modes of operation.
2. Description of the Prior Art
Subterranean slurry mining of phosphates or the like is broadly known in the art as evidenced by U.S. Wenneborg et al Pat. Nos. 3,730,592 and 3,747,696 which issued on May 1, 1973 and July 24, 1973, respectively, and are assigned to the assignee of the present invention. The disclosures of both of these patents are incorporated by reference herein.
The modified embodiment of the device disclosed in Wenneborg et al U.S. Pat. No. 3,747,696 is the most pertinent prior art embodiment and comprises a combination slurry drilling and mining apparatus which may be changed between its drilling mode of operation and its mining mode of operation to mine several different layers of ore without requiring that the apparatus be pulled out of the hole or well. However, the hydraulic control system for changing the several valves from the drilling mode to the mining mode requires a positive pressure of about 2000 psig in the prior art device which is much greater than the approximately 1000 psig mining pressure. The prior art hydraulic control system thus requires additional high pressure pumping equipment, and is also subject to damage due to the very high control pressures and "water hammer" type forces which may be applied to the system.
Wenneborg et al U.S. Pat. No. 3,730,592 discloses a method which contemplates the use of surface controlled pressures equal to or in excess of the drilling pressure for shifting the mining nozzle, the eductor nozzle, and the drill bit foot valve between the drilling mode and the mining mode. In addition, the patentee discloses the use of control pressures which lie in a range between the drilling pressure and the mining pressure for modulating the mining nozzle. Modulation of the mining nozzle is effective to control the cavity pressure, and also the liquid level in the mined cavity to vary the mining conditions for the particular strata being mined.
U.S. parent and divisional Pat. Nos. 3,155,177 and 3,316,985 which issued to A. B. Fly on Nov. 3, 1964 and May 2, 1967, respectively, disclose a method and apparatus for under-reaming or slurry mining a well and can also be controlled to alternately bore deeper and mine other strata in the well after the first boring and mining operations have been completed. Valves operated by electric motors located within the tool string convert the apparatus from a drilling operation to a mining operation. The amount of force that can be applied to convert the apparatus from the drilling operation to the mining operation is, accordingly, limited by the size of the electric motors that can fit within the tool string.